The invention pertains to a hydrogen electrode in rod form, especially for use as a reference electrode in electrochemical measurements or as a pH measuring electrode, which contains the integrated hydrogen supply in the form of a hydrogen generation cell of the type described in DE-PS 35 32 335 and makes it available during operation in an amount adequate for the given function.
DE-PS 35 32 335 discloses an electrochemical cell for generating hydrogen and/or oxygen which is generally comprised of an anode, a cathode and an aqueous electrolyte in a metal and/or plastic housing. The anode is composed of a substance subject only to electrochemical oxidation in its initial state. The cathode is either a hydrogen releasing electrode, or is composed of an electrochemically reducible substance. The cell contains an oxygen releasing electrode, and either hydrogen or oxygen can be formed responsive to a flow of current. The applied current results in a flow of gas from the pores of what essentially constitutes a gas diffusion electrode, which functions either as a cathode or as an anode, and is permitted to pass to the outside of the cell through the pores of a hydrophobic diffusion membrane. A preferred gas generating cell includes a metal (preferably zinc) anode, a hydrogen cathode composed of a layer of metal and/or carbon powder with a PTFE binder on a metal mesh, laminated with a porous PTFE film, and an alkaline electrolyte. The cell can be used to produce either hydrogen or oxygen in amounts proportional to the current which is applied.
The hydrogen electrode is of central importance in electrochemical measuring technology. This is apparent from the so-called pH value, i.e., the negative of the hydrogen ion exponent. It is obtained by taking the common logarithm of the concentration (or the activity) of the hydrogen ions in a solution. This is the most commonly used quantity for characterizing aqueous solutions.
The measurement is generally performed by immersing a platinized platinum foil into the solution and causing hydrogen to flow around it. It then represents one potential pole of a measuring cell, whose other pole is a reference electrode of the same or different type in a standard solution of known pH, which is galvanically connected with the test solution by an electrolytic switch.
The hydrogen electrode is used even more commonly as an unloaded reference electrode in electrochemical measuring cells. In this case, the hydrogen-covered platinum electrode is immersed in a so-called Luggin capillary, whose opening is located directly in front of the test electrode, with which the unloaded reference electrode forms a galvanic cell. The potential changes of the galvanic cell are due solely to the potential changes of the test electrode during current flow or otherwise changing test conditions.